1. Field of the Invention
The present invention relates to the preparation of spheroidal alumina particulates shaped by drop coagulation, and to the utilization of such particulates as catalyst supports.
2. Description of the Prior Art
It is known to this art, from published European patent Application No. 15,801, assigned to the assignee hereof, to prepare spheroidal alumina particles having bifold porosity by the method designated "oil drop" or "drop coagulation".
The process described in the aforenoted application comprises a mixture, at a pH of less than about 7.5, of a sol of ultra-fine boehmite or of psuedo-boehmite with spheroidal alumina particulates in a proportion ranging from 30 to 95% by weight. The boehmite sol has a concentration ranging from 5 to 25%. The spheroidal alumina particles are in the form of at least one of the phases included in the group consisting of eta, gamma, delta and theta. Same have a micropore volume ranging from 0.4 to 1 cm.sup.3 /g; their specific surface area ranges from 100 to 350 m.sup.2 /g and their diameter ranges from 1 to 50 microns; their shaping into the spheroidal form and the gelation of the droplets of the mixture, the recovery of the gelled spheres, and their drying and calcination at a temperature ranging from 550.degree. to 1100.degree. C. Cf. U.S. Pat. No. 4,315,839.
The shaping into the spheroidal form and the gelation of the droplets employed in the process is effected by dripping droplets of the mixture into a column containing an upper phase consisting of petroleum and an aqueous lower phase consisting of an ammonia solution. The shaping process takes place in the upper phase and the gelation essentially in the lower phase. The temperature of the petroleum is typically close to ambient temperature. The pH of the ammonia solution is maintained at a value higher than approximately 9. The retention time of the droplets in the ammonia is a few minutes and is generally less than 15 minutes. Under these conditions, the spheroidal particles collected are sufficiently solid and are not deformed by subsequent manipulations.
The aforesaid process has numerous advantages. In particular, it makes it feasible to begin with readily accessible raw materials which are easy to prepare, and it permits the obtention of lightweight products without the need to use pore-forming agents. Finally, it makes it possible to eliminate an aging stage of the spheroidal particles in ammonia after their gelation.